The long-term goal of this project is to elucidate the mechanism of action and physiologic function of heparin cofactor H (HCII). HCII is an inhibitor of thrombin that is present in plasma at a concentration of -1 uM. The anticoagulant activity of HCII is greatly increased by heparin or dermatan sulfate, and dermatan sulfate proteoglycans on the surface of fibroblasts and smooth muscle cells stimulate HCH. Previously, cDNA and genomic clones for human and murine HCII were isolated, recombinant HCII was expressed in E. coli, site-directed mutagenesis was performed to identify important amino acid residues that interact with thrombin and glycosaminoglycans, and the structure of a high-affinity hexasaccharide that binds HCII in porcine skin dermatan sulfate was identified. Although the function of HCII in vivo remains unknown, indirect evidence suggests that HCII activity increases during pregnancy and perhaps serves to inhibit coagulation of maternal blood in the placenta. In addition, the presence of HCII in the intima of normal human arteries and the altered composition of dermatan sulfate (with reduced HCII-stimulating activity) in atherosclerotic lesions provide circumstantial evidence of a role for HCII in atherogenesis. By means of targeted gene disruption in embryonic stem cells, a murine model of HCII deficiency has been developed. The following specific aims are proposed: (1) Determine the effects of HCII deficiency on hemostasis, atherogenesis, wound repair, and inflammation in the mouse. (2) Determine the location of endogenous HCH in human and murine tissues by immunohistochemical methods and identify binding Sites for exogenous HCII in tissue sections. (3) Characterize the oligosaccharide structures in glycosaminoglycans derived from placenta and other tissues that are required for interaction with HCII. (4) Determine the prevalence of HCII deficiency in patients with atherosclerosis. New information about the structure, mechanism of action, and function of HCII in vivo will provide a better understanding of the regulation of thrombin activity under normal and pathologic conditions.